None.
1. Field of Invention
This invention relates to catalyzed diesel particulate matter exhaust filters and more particularly to a catalyzed diesel particulate exhaust filter which includes a porous filter substrate and a catalytic material, wherein the catalytic material is comprised of an alkaline earth metal vanadate and a precious metal. The invention also includes a process of manufacture of the catalyzed exhaust filter and a process of use of that catalyzed exhaust filter.
2. Background Art
Diesel engines, as a result of their operating characteristics, emit very fine particles. The particulate materials are referred to as particulate matter (PM). In addition to the emission of particulate materials, other types of gaseous compounds are also emitted by diesel engines, such as hydrocarbons, sulfur oxides, nitrogen oxides and carbon monoxide.
It is well known in the art to provide diesel engines with exhaust filters which trap particulate materials from exhaust gas streams during engine operation. These filters are generally made of a porous, solid material having a plurality of pores extending therethrough and small cross-sectional sides, such that the filter is permeable to the exhaust gas which flows through the filter and yet capable of restraining most or all of the particulate materials from passing through the filter with the exhaust gas. As the mass of collected particulate materials increases in the filter, the flow rate of the exhaust gas through the filter is gradually impeded, resulting in an increased back pressure within the filter, which results in a reduced engine efficiency. Conventionally, when the back pressure reaches a certain level, the filter is either discarded, if it is a replaceable filter, or removed and regenerated by burning the collected particulate materials off at a temperature in excess of about 600-650xc2x0 C. so that the filter can be reused. Regeneration of filters in situ can sometimes be accomplished by periodically enriching the air fuel mixture. This enrichment produces a higher exhaust gas temperature. This higher exhaust temperature burns off the particulate materials contained in the filter. The concept of a filter which will regenerate at a temperature lower than 600-650xc2x0 C. is disclosed in various patents, for example, U.S. Pat. Nos. 5,100,632 and 4,477,417.
The composition of diesel exhaust particulate filters has been the subject of a number of patents. Many of these patents disclose the use of a combination of particular vanadium compounds and a platinum compound which are washcoated onto a support material. The washcoated support material is then heated to secure the washcoat material to the support material. For example, U.S. Pat. No. 6,013,599 discloses a diesel exhaust particulate filter which can be regenerated in situ, which is formed from a porous refractory support material onto which a washcoating is secured, wherein the washcoating in one embodiment is formed by mixing an acidic iron-containing compound and a copper-containing compound, adding an aqueous alkali metal salt solution and an acidic vanadium-containing compound and finally adding to that mixture an alkaline earth metal compound slurry.
U.S. Pat. No. 4,510,265 discloses a coated diesel exhaust particulate filter formed by coating a solution comprising a platinum group metal and a silver vanadate onto a ceramic monolithic support material. A process of manufacture of a catalyst coating for a diesel exhaust particulate filter containing a silver vanadate is also disclosed by U.S. Pat. No. 4,477,417.
Another diesel exhaust particulate filter is disclosed in U.S. Pat. No. 4,588,707 in which a catalytically active substance formed from lithium oxide, copper chloride, a vanadium oxide/alkali metal oxide combination or precious metal materials is coated onto a filter substrate. Another vanadium-based material for coating a filter for the purification of exhaust gases from diesel engines is disclosed in U.S. Pat. No. 4,828,807.
An open cell monolithic catalyst for the purification of diesel exhaust gases, which monolith is coated with oxides containing vanadium and platinum group metals as active components is disclosed in U.S. Pat. No. 5,514,354. See also U.S. Pat. No. 5,157,007.
Another catalyst for purifying diesel exhaust gases containing platinum and vanadium oxide is disclosed in U.S. Pat. No. 4,617,289. See also U.S. Pat. Nos. 5,911,961, 4,902,487, 4,515,758, 5,884,474, 5,746,989 and 4,900,517 for other catalysts for purifying exhaust streams.
Another exhaust gas purifying catalyst comprising copper, vanadium, a precious metal, such as platinum, rhodium or palladium, and a transition metal selected from the group consisting of zirconium, aluminum, nickel, iron, manganese, chromium, zinc, lead or certain other metals coated on a filter substrate is disclosed in U.S. Pat. No. 4,711,870. See also U.S. Pat. No. 4,759,918.
U.S. Pat. No. 5,100,632 discloses another catalyzed diesel exhaust particulate filter comprising a platinum group metal and an alkaline earth metal oxide, preferably magnesium oxide, wherein the materials are impregnated on a monolithic substrate. The use of vanadium is not disclosed.
A method of cleaning nitrogen oxide containing exhaust gases is disclosed in U.S. Pat. No. 5,213,781, wherein a catalyst is supported on a ceramic layer, wherein the catalyst consists essentially of at least one of an alkali metal, copper and vanadium and at least one rare earth element. See also U.S. Pat. No. 5,340,548.
Other diesel exhaust gas purification catalysts are disclosed in U.S. Pat. Nos. 5,000,929, 5,330,945 and 5,294,411.
While these patents disclose a number of different compositions of material for use as filters for diesel particulate matter, there are still significant problems associated with increased pressure drop during use of these filter. Further, the amount of pressure drop may increase dramatically depending upon the catalyst loading of the substrate material. In addition, some of the diesel combustion catalysts do not have good sulfur poison resistance and can be deactivated if the temperature of the exhaust gas is too high.
Accordingly, it is an object of the invention to produce a filter for diesel particulate matter.
It is a further object of the invention to disclose a diesel particulate matter exhaust filter produced from a porous filter substrate which is impregnated with a catalytic material.
It is a further object of the invention to disclose a diesel particulate matter exhaust filter produced from a porous filter substrate impregnated with a catalytic material, wherein the catalytic material comprises an alkaline earth metal vanadate and a precious metal.
It is a further object of the invention to disclose a catalyzed diesel particulate matter exhaust filter produced from a porous filter substrate impregnated with magnesium, calcium and/or barium vanadate and platinum.
It is a further object of the invention to disclose a process for the manufacture of a diesel exhaust filter wherein a porous filter substrate is impregnated with a catalytic material comprising an alkaline earth metal vanadate and a precious metal.
It is a further object of the invention to disclose a process of use of the catalyzed diesel particulate matter exhaust filter, wherein the exhaust filter comprises a porous filter substrate impregnated with a catalytic material comprising an alkaline earth metal vanadate and a precious metal whereby during use there is a reduced back pressure drop and high thermal stability.
These and other objects of the invention will be apparent from the catalyzed diesel particulate matter exhaust filter of the invention and the process of manufacture and process of use of that exhaust filter.
The present invention comprises a catalyzed diesel particulate matter exhaust filter comprising a porous filter substrate impregnated with a catalytic material comprising an alkaline earth metal vanadate, preferably a magnesium, calcium or barium vanadate, and a precious metal, preferably platinum.
The invention further comprises a process for forming a diesel particulate matter exhaust filter comprising forming a porous filter substrate and impregnating that substrate with a catalytic material, wherein the catalytic material comprises an alkaline earth metal vanadate, preferably magnesium, calcium or barium vanadate, and a precious metal salt, preferably a platinum salt, which catalytic material is then reduced.
The invention further comprises a method of filtering particulate matter from a diesel exhaust using a diesel exhaust filter comprising passing the diesel exhaust over a diesel exhaust filter comprising a porous filter substrate impregnated with a catalytic material, wherein the catalytic material comprises an alkaline earth metal vanadate, preferably magnesium, calcium or barium vanadate, and a precious metal, preferably platinum.